1. Field of the Invention
This invention pertains generally to the field of mechanical printing devices, as opposed to photostatic printing or copying devices, in which a page or form is typically advanced lengthwise in a stepping manner. More particularly, this invention relates to the mechanism which disengages the paper feed driven shaft from the drive mechanism thereby permitting the shaft to be freely rotated to effect a fine adjustment of the vertical position of the paper.
2. Prior Art
The present invention is intended to operate in high speed printing devices. In the typical high speed printing device, the paper form on which the printing takes place, is advanced vertically down its length by a form advancing mechanism which is activated by a driven shaft powered by a drive means. Generally, the driven shaft is horizontally oriented. The operation of one such form advancing mechanism is more thoroughly described in U.S. Pat. No. 3,452,853 issued July 1, 1969 to Stuart Mabon. The form advancing mechanism mentioned herein is similar but not identical to the referenced mechanism. Generally to advance the form, a signal is transmitted to a drive means, which may be a stepping motor means, which rotates a driven shaft causing the form advancing mechanism to engage and advance the form, as in the U.S. Pat. No. 3,452,853 to Stuart Mabon. In order to advance the form in other than a stepping manner, the driven shaft must be longitudinally displaced so as to disengage it from the stepping or other drive means and the driven shaft must then be manually rotated to the desired position. Thus, two motions are required, one longitudinally directed, the other rotationally directed.
There are several prior art mechanisms designed to produce these two motions and thereby permit fine adjustment of the vertical position of a form within a printing device.
One popular mechanism comprises a knob with a "button" in the end of the knob. This type is commonly used on typewriters. The longitudinal displacement is achieved by depression of the "button" in a direction coincident with the axis of the driven shaft. The rotation is achieved by rotating the knob while the button is depressed. This type of mechanism requires the coordinated use of the thumb (to depress the button) and likely two fingers (to rotate the knob). When the botton of this mechanism is released, the driven shaft is automatically reengaged with the drive means.
Another prior art mechanism also common on typewriters is such that the knob itself also serves the function of the button. A single knob is pushed (or pulled) in a direction coincident with the longitudinal axis of the driven shaft thereby laterally displacing the shaft and disengaging it from the drive means. The knob is then freely rotatable so as to advance and finely adjust the vertical position of the form. Again, the use of more than one digit is required, and with this mechanism it is likely that four or maybe all five digits of the operator's hand will be used. With this mechanism the driven shaft is reengaged with the drive means only after the entire knob is pulled (or pushed) back to its original position.
A third mechanism which is designed to effect a longitudinal displacement of the driven shaft followed by rotation of the shaft is a rather complicated device comprising a knob having levers or handles which are squeezed, pushed, or pulled to produce the longitudinal displacement and then the entire knob is rotated to finely adjust the vertical position of the form. This mechanism also requires the use of more than one digit and the application of forces in different directions. With this mechanism the driven shaft is automatically reengaged with the drive mechanism upon release of the levers or handles.
Each of these prior art mechanisms suffer from some common disadvantages. Each mechanism requires more than one motion of the hand or fingers to make the fine adjustment. A first horizontal motion is required to disengage the driven shaft from the drive mechanism. A second rotational motion is required to effect the fine adjustment of the vertical position of the form. Another common disadvantage is that the operator must apply a force in a difficult and unnatural direction. Generally the operator of the printing device is seated facing the device. To effect the longitudinal displacement of the driven shaft, the operator must extend his arm from his body and generate a horizontal force of sufficient magnitude to activate the mechanism. To generate a horizontal force directed across the body is in itself an unnatural and uncomfortable action. Additionally, if the operator is seated in a swivel chair, unless his feet are firmly planted on the floor, he may be caused to rotate slightly in his chair as a reaction to generating the force. Another disadvantage is that because the arm of the operator is likely extended so as to reach the machine, the operator must overcome the substantial mechanical disadvantage of his extended arm. That is, significant effort of the operator's pectoral muscles must be exerted to generate a relatively small force at the end of his fingers.
Two of these prior art mechanisms exhibit a third disadvantage. These mechanisms require the operator to grasp the device in a specific place or to apply a force at a small specific location. A specific button must be pushed, or a specific lever must be thrown.
Each of these prior art mechanisms requires the use of more than one digit in order to disengage the driven shaft from the drive means and advance the paper.
It is thus an object of the present invention to provide a mechanism, to disengage the driven shaft from the motor or other drive means thereby permitting fine adjustment of the vertical position of the form in the printing device, which does not require the operator to exert a horizontal force directed across the body of the operator.
It is a further object of the present invention to provide such a mechanism which can effect the fine vertical adjustment of the form in response to a single motion of a single digit of the operator.
It is another object of the present invention to provide such a mechanism which can effect the fine vertical adjustment of the form in response to a force applied over a wide range of locations on the mechanism and applied in any one of a plurality of directions.